In a spiral forming manufacturing process, a sheet of steel is fed into a mill and continuously roll-formed into a desired shape. For example, using this technique a cylinder or a conical shape can be formed by feeding sheets of suitably shaped material into the mill and continuously joining the curved, roll-formed material along a spiral edge as the material exits the mill. While a variety of useful structures such as steel towers for wind turbines can be fabricated using this technique, transitions between the sheets used to form these structures present certain challenges with respect to meeting manufacturing tolerances and efficient use of material in the final structures.